DRIVE ASSEMBLY FOR AN ELECTRIC VEHICLE AND METHOD FOR OPERATING A DRIVE ASSEMBLY

Abstract

The disclosure relates to a drive assembly for an electric vehicle and to operation of a drive assembly. The drive assembly can comprise an electric drive machine with three phase strands. The drive assembly can comprise a switching means being configured for selectively switching the three phase strands in a delta configuration or in a star configuration. The drive assembly can also comprise a battery unit, wherein the battery unit comprises a plurality of battery cells and a plurality of cell-level control units. Each of the cell-level control units can be electrically connected to an associated battery cell out of the plurality of battery cells, or to an associated group of battery cells out of the plurality of battery cells, and each of the cell-level control units can comprise a cell-level inverter unit.

Claims

1. A drive assembly for an electric vehicle, comprising: an electric drive machine comprising three phase strands; a switching means electrically connected to the electric drive machine and configured for selectively switching the three phase strands in a delta configuration or in a star configuration; and a battery unit electrically connected to the electric drive machine via the switching means, wherein the battery unit comprises a plurality of battery cells and a plurality of cell-level control units, wherein each of the cell-level control units is electrically connected to an associated battery cell out of the plurality of battery cells, or to an associated group of battery cells of the plurality of battery cells, and wherein each of the cell-level control units comprises a cell-level inverter unit configured to transform a direct current being provided by the associated battery cell, or the associated group of battery cells, into an alternating current of adjustable voltage.

2. The drive assembly of claim 1, wherein the plurality of battery cells and corresponding cell-level control units are arranged in a number of battery cell strings, and wherein the number of battery cell strings correspond to a number of phase strands of the electric drive machine.

3. The drive assembly of claim 2, wherein each of the battery cell strings comprises a first end and a second end, wherein the second end is arranged opposite to the first end, and wherein all first ends are electrically connected to the switching means, or all second ends are electrically connected to each other at a neutral point.

4. The drive assembly according to claim 2, wherein each of the battery cell strings comprises 1 to 500 battery cells.

5. A method for operating a drive assembly, comprising: operating the drive assembly in a first operational mode, wherein the first operational mode comprises connecting phase strands of an electric drive machine in a delta configuration by using a switching means, and providing a first set of alternating currents of a first voltage to the electric drive machine by a battery unit electrically connected to the electric drive machine via the switching means, wherein the battery unit comprises a plurality of battery cells and a plurality of cell-level control units; or operating the drive assembly in a second operational mode, wherein the second operational mode comprises connecting the phase strands of the electric drive machine in a star configuration by using the switching means, and providing a second set of alternating currents of a second voltage to the electric drive machine by the battery unit.

6. The method of claim 5, wherein providing a first set of alternating currents of a first voltage or providing a second set of alternating currents of a second voltage comprises electrically connecting a sub-set of the plurality of battery cells to the electric drive machine.

7. The method of claim 5, wherein providing a first set of alternating currents of a first voltage or providing a second set of alternating currents of a second voltage comprises electrically connecting all battery cells of the plurality of battery cells to the electric drive machine.

8. The method of claim 5, wherein, in the first operational mode and in the second operational mode, the electric drive machine is operated at the same load point.

9. The method of claim 5, wherein the first operational mode is a default operational mode.

10. The method of claim 5, wherein a ratio between the first voltage and the second voltage is 1.5 to 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Examples of the disclosure will be described in the following with reference to the following drawings.

[0031] FIG. 1 shows a drive assembly according to the present disclosure which may be operated using a method for operating a drive assembly according to the present disclosure,

[0032] FIG. 2 shows the drive assembly of FIG. 1 from an electric perspective, wherein phase strands of the electric drive machine are in a delta configuration and wherein a switching means of the drive assembly is not represented,

[0033] FIG. 3 shows the drive assembly of FIG. 1 from an electric perspective, wherein phase strands of the electric drive machine are in a star configuration and wherein a switching means of the drive assembly is not represented, and

[0034] FIG. 4 shows a cell-level control unit and an associated group of battery cells of the drive assembly of FIGS. 1 to 3.

DETAILED DESCRIPTION

[0035] The figures are merely schematic representations and serve only to illustrate examples of the disclosure. Identical or equivalent elements are in principle provided with the same reference signs.

[0036] FIG. 1 shows a drive assembly 10 for an electric vehicle.

[0037] The drive assembly 10 comprises an electric drive machine 12 which has three phase strands 12a, 12b, 12c in the present example (see also FIGS. 2 and 3). Thus, the electric drive machine 12 is a three phase AC electric machine.

[0038] The electric drive machine 12 may be a synchronous machine.

[0039] In order to provide the necessary electric power to the electric drive machine 12, the drive assembly 10 comprises a battery unit 14.

[0040] The battery unit 14 is electrically connected to the electric drive machine 12.

[0041] The battery unit 14 comprises a plurality of battery cells 16 and a plurality of cell-level control units 18 which are arranged in a number of battery cell strings 20a, 20b, 20c which corresponds to the number of phase strands 12a, 12b, 12c of the electric drive machine 12.

[0042] Thus, in the present example, the battery unit 14 comprises three battery cell strings 20a, 20b, 20c (see also FIGS. 2 and 3).

[0043] For reasons of better visibility, only some of the battery cells 16 carry a reference sign.

[0044] Each of the battery cell strings 20a, 20b, 20c is electrically connected to one phase strand 12a, 12b, 12c via a corresponding first end of the battery cell string 20a, 20b, 20c.

[0045] Each of the battery cell strings 20a, 20b, 20c also comprises a second end which is arranged opposite the corresponding first end.

[0046] All second ends are electrically connected to each other at a neutral point 22.

[0047] Each of the battery cell strings 20a, 20b, 20c is configured to provide electric power to the associated phase strand 12a, 12b, 12c.

[0048] In the example shown in the Figures, each of the battery cell strings 20a, 20b, 20c comprises 96 battery cells 16 which are electrically connected in series.

[0049] A group of battery cells 16 and a corresponding cell-level control unit 18 is shown in FIG. 4.

[0050] In the example shown, the group of battery cells 16 comprises four battery cells 16 which are electrically connected in series. The ends of this electrical series connection are electrically connected to the cell-level control unit 18.

[0051] It is noted that, in an alternative in which a single battery cell 16 is electrically connected to an associated cell-level control unit 18, the connection terminals or poles of the battery cell 16 are electrically connected to the cell-level control unit 18.

[0052] Each of the cell-level control units comprises a cell-level inverter unit 24 being configured to transform a direct current being provided by the associated battery cell 16 or the associated group of battery cells 16 into an alternating current of adjustable voltage.

[0053] To this end and/or other various ends, the cell-level inverter unit 24 uses the DC voltage of the associated group of battery cells 16 as an input voltage.

[0054] As an output interface, the cell-level inverter unit 24 has two output terminals 24a, 24b which also serve as the output terminals of the cell-level control unit 18.

[0055] Thus, the output terminals 24a, 24b are used for connecting the cell-level control unit 18 and the associated single battery cell 16 or the associated group of battery cells 16 to one or two neighboring cell-level control units 18 within the respective battery cell string 20a, 20b, 20c.

[0056] In various examples, the electric connection of the battery unit 14 to the electric drive machine 12 is not direct, instead via a switching means 26.

[0057] This means that the switching means 26 is electrically connected to the battery unit 14 and to the electric drive machine 12.

[0058] The switching means 26 is configured for selectively switching the three phase strands 12a, 12b, 12c in a delta configuration (cf. FIG. 2) or in a star configuration (cf. FIG. 3).

[0059] The electric drive assembly 10 can be operated using a method for operating a drive assembly 10.

[0060] According to the method, the drive assembly 10 may be operated in a first operational mode.

[0061] In the first operational mode, the phase strands 12a, 12b, 12c of the electric drive machine 12 are connected in a delta configuration by using the switching means 26 (cf. FIG. 2).

[0062] In the first operational mode, it is sufficient to just use a sub-set of battery cells 16 of each of the battery cell strings 20a, 20b, 20c. This means that just the battery cells 16 pertaining to the sub-set are electrically connected to the electric drive machine 12. The remaining battery cells 16 are bypassed using the corresponding cell-level control unit 18.

[0063] The battery cells 16 of the sub-set of each battery cell string 20a, 20b, 20c provide a voltage being denoted UA.

[0064] Using the cell-level control units 18 each of the phase strands 12a, 12b, 12c is provided with an AC signal being characterized by a voltage U.sub.V and a current I.sub.A.

[0065] These characteristics are to be understood as effective or root mean square values.

[0066] Since the delta configuration is called a first operational mode, the alternating currents provided to the phase strands 12a, 12b, 12c of the electric drive machine 12 by the battery unit 14 may be designated as a first set of alternating currents.

[0067] In various examples, the first operational mode is a default operational mode.

[0068] According to the method, the drive assembly 10 may be operated in a second operational mode.

[0069] In various examples, the second operational mode is an alternative to the first operational mode.

[0070] In the second operational mode, the phase strands 12a, 12b, 12c of the electric drive machine 12 are connected in a star configuration by using the switching means 26 (cf. FIG. 3).

[0071] It is noted that a load point is not altered when switching from the first operational mode to the second operational mode, or vice-versa. Thus, in the first operational mode and in the second operational mode, the electric drive machine 12 is operated at the same load point.

[0072] In contrast to the first operational mode, in the second operational mode, all battery cells 16 of all battery cell strings 20a, 20b, 20c are used. This means that all battery cells 16 of the battery unit 14 are electrically connected to the electric drive machine 12.

[0073] The battery cells 16 of each battery cell string 20a, 20b, 20c now provide a voltage of U.sub.A′ √{square root over (3)}, e.g., a higher voltage than in the first operational mode.

[0074] This has the effect that again, the same voltage U.sub.V can be provided to each of the phase strands 12a, 12b, 12c.

[0075] Moreover, in the second operational mode, the current for each connection point of the phase strands 12a, 12b, 12c can be reduced to I.sub.A/√{square root over (3)}.

[0076] As before, the voltage U.sub.V and the current I.sub.A are to be understood as effective or root mean square values.

[0077] Since the star configuration is called a second operational mode, the alternating currents provided to the phase strands 12a, 12b, 12c of the electric drive machine 12 by the battery unit 14 may be designated as a second set of alternating currents.

[0078] Due to the reduced current in the second operational mode, also the electric losses in the electric drive unit 10 are reduced.

[0079] The electric losses may be generally described as a power loss P.sub.loss which is a function of the electric resistance R and the current I:

P.sub.loss=R*I.sup.2

[0080] In the context of the electric drive assembly 10, the electric resistance is a combination of an internal electric resistance R.sub.cells of the battery cells, an electric resistance R.sub.inv of the cell-level control units, an electric resistance R.sub.cable of the cabling, and an electric resistance R.sub.bus of the busbars used in the battery unit 14. Thus, the above equation can be rewritten as:

P.sub.loss=(R.sub.cells+R.sub.inv+R.sub.cable+R.sub.bus)*I.sup.2

[0081] The fact that the losses are reduced increases the overall efficiency of the electric drive assembly 10. Consequently, the second operational mode may be designated as an energy saving mode or an eco-mode.

[0082] The electric drive assembly 10 may be triggered to operate in the first or second operational mode by a user. In this regard, the operational mode may be selected manually.

[0083] Alternatively, or additionally, the second operational mode may be chosen automatically by a corresponding control unit of the vehicle.

[0084] Other variations to the disclosed examples can be understood and effected by those skilled in the art in practicing the claimed disclosure, from the study of the drawings, the disclosure, and the appended claims. In the claims the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items or steps recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

[0085] 10 drive assembly [0086] 12 electric drive machine [0087] 12a phase strand [0088] 12b phase strand [0089] 12c phase strand [0090] 14 battery unit [0091] 16 battery cell [0092] 18 cell-level control unit [0093] 20a battery cell string [0094] 20b battery cell string [0095] 20c battery cell string [0096] 22 neutral point [0097] 24 cell-level inverter unit [0098] 24a output terminal [0099] 24b output terminal [0100] 26 switching means